HOW STORMS DEVELOP: Storm clouds form as moisture evaporates from the earth into the atmosphere. The air cools off rapidly as it reaches higher altitudes. Sometimes a cold front -- where the cold air from one air mass meets the surrounding air -- will force warm, moist air upward into the colder air. This cools the water vapor and it condenses onto dust and dirt particles in the air, called condensation nuclei, collectively forming clouds. Nuclei made of ice are usually present before rain or snow fall. The process continues: more and more water vapor turns into liquid and the moist air gets warmer and rises higher and higher. A thunderstorm results. New research demonstrates that most condensation nuclei are actually biological in origin, with bacteria at the core.
WHAT'S THE FORECAST: Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. For millennia people have tried to forecast the weather. In 650 BC, the Babylonians predicted the weather from cloud patterns. In about 340 BC, Aristotle described weather patterns in Meteorologica. Chinese weather prediction lore extends at least as far back as 300 BC. Ancient weather forecasting methods usually relied on observed patterns of events. For example, it might be observed that if the sunset was particularly red, the following day often brought fair weather. This experience accumulated over the generations to produce weather lore. Today, weather forecasts are made by collecting data about the current state of the atmosphere and using computer models of the atmospheric processes to project how the atmosphere will evolve.
The American Meteorological Society and the American Geophysical Union contributed to the information contained in the TV portion of this report.